1. Field of the Invention
This invention generally relates to valve mechanisms for controlling the air pressure in an air brake system used on railroad trains and, more particularly, to a motor driven valve mechanism which is capable of rapidly venting air in an air pipe to the atmosphere in an emergency situation.
2. Description of the Prior Art
Air brake systems used on railroad rolling stock comprise a pressurized system which normally holds the brake shoes from contacting the brake drums on the individual trucks of the various cars. Pressure is supplied by an air pipe that, when coupled from car to car, extends from the locomotive to last car of the train. Once the air pipe is pressurized in a yard, the pressure is maintained by a locomotive driven compressor. The brakes at the individual trucks are applied in a controlled manner by reducing the pressure in the air pipe slowly. The brakes at the individual trucks are rapidly applied in an emergency operation by venting the air pipe to atmosphere.
U.S. Pat. No. 4,641,892 to Schmid shows remote control of air brakes during an emergency situation. Telemetry equipment directs a solenoid operated pilot valve actuator to open when the train needs to be stopped in an emergency. Operation of the solenoid creates a difference in pressure between the primary or valve seating side of a quick exhaust valve and its secondary side. The difference in pressure unseats the quick exhaust valve and allows the air pipe to be vented to atmosphere.
A solenoid valve, as shown in the Schmid patent, is particularly disadvantageous for use on railroad trains because solenoid type valves are not very tolerant of debris. Most trains, after a long period of use, tend to have rusted brake pipes. The presence of rust and corrosion may hinder the emergency operation of the brakes in Schmid.
U.S. Pat. No. 4,487,070 to Pomeroy shows an apparatus for remotely monitoring the air pressure of the air pipe at the end of a train. The information, including emergency warning signals, is telemetered to the engineer in the locomotive.
A two-way link between the end of the train and the locomotive has been proposed for allowing the engineer to control certain functions at the end of the train. These functions may include emergency operation of the brakes, or testing operations to determine if the air pressure sensors or brakes are operable. While the Schmid valve actuator might be controlled remotely from the locomotive cab using such a two-way link, the only function of this valve actuator is to vent the air pipe to atmosphere in an emergency application of the brakes.